1. Field of the Invention
The present invention relates to the field of power dimmers for controlling a load supplied from an A.C. voltage, generally the mains voltage of the electric supply system.
2. Discussion of the Related Art
Among known power dimmers, two MOS power transistors assembled in anti-series with the load to be controlled can be used, each transistor being in antiparallel with a high-voltage diode and being dedicated to one of the halfwaves of the supply voltage. To properly control these transistors, a first known technique consists of using a microprocessor to execute a digital control. A second known (analog) technique uses two operational amplifiers and requires two additional high-voltage diodes to detect the zero crossing of the mains voltage.
One problem linked to the use of two transistors in anti-series is that it is necessary to control these transistors at a frequency which is twice the supply voltage frequency (once for each halfwave).
Another problem is that the turning-off at the current zero or the turning-on at the voltage zero is not natural and must be controlled.